Autoreload

[333fred]

This PR adds autoreloading of test assemblies (on by default), using the FileSystemWatcher Windows api to do the notification.

• A new setting has been added, "Auto Reload Test Assemblies"
• When a new assembly is added, the MainViewModel tells the ITestAssemblyWatcher to watch it. When enabled, the MainViewModel provides a callback that the watcher will call when the file is created or written to.
• When a test assembly is updated, it's added to a list of assemblies to be autoreloaded. Because file operations can actually cause many updates to be sent in quick succession, and building one test assembly likely means another might be built very soon, we batch updates. We wait 100 ms after receiving an update notification to ask for reload, resetting that timer every time a new update is requested.

[333fred]

@Pilchie does appveyor not have 2017?

[Pilchie]

Not sure. If it does, my config might need tweaking. Will look tomorrow.

[Pilchie]

Alternatively, you could reference the compiler nuget.

[333fred]

@Pilchie from what I saw, they do have an image, it should be as simple as selecting that as the base image.

[sharwell]

@333fred You can set the image in appveyor.yml if you add one.

[333fred]

Just moved to the compilers nuget package. I don't know the rest of Kevin's appveyor settings, and from what I see of the docs the yaml will override them.